This invention relates to a power tong device. More particularly it concerns a power tong device comprising a frame with a power tong and a holding tong and also a drive gear for the power tong, and wherein the power tong relative to the holding tong is displaceable along its rotational axis.
Known power tong devices for use such as on a drill floor, comprises a driven power tong and a holding tong working about a common rotational axis, as the central axis also constitutes the power tong rotational axis.
When a pipe joint shall be connected to a pipe string, it is common to hold the upper pipe string socket fixedly in the holding tong. The pipe joint pin is displaced down toward the socket where the pipe joint is gripped by the power tong. The power tong together with the pipe joint is displaced in a direction toward the socket while the power tong rotates the pipe joint about its rotational axis.
The pin joint threads thereby enter the socket threads and are screwed into these with the desired torque.
Experience shows that a threading operation of this kind may damage the thread if the pipe joint is not concentric with the rotational axis when the pin joint threads enter the socket.
The reason is thought to be that when the power tong positions the pipe joint centrally by its grip on the pipe joint, an angular deviation between the pipe joint and the rotational axis may entail that so large strains are inflicted on the threads, that they are damaged.
Thread damage may cause the pipe string to have to be pulled sufficiently up to change out the damaged pipe joint, causing both extra work and unnecessary cost.